When you have a quality starting cornerback you secured with a first-round draft pick, you don’t allow him to walk out the door. That was the thinking of the Giants, who picked up the fifth-year option for Prince Amukamara, which puts him under contract through the 2015 season.

The Giants had to decide before Saturday whether to exercise the fifth-year option on Amukamara or allow him to become a free agent after the 2014 season. By picking up the option, Amukamara will make $6.898 million for the 2015 season.

Amukamara was the best cornerback remaining on the roster before the free-agent signing of Dominique Rodgers-Cromartie, who was given a five-year, $35 million deal. Rodgers-Cromartie was immediately anointed as the No. 1 corner on the team by coach Tom Coughlin.

Amukamara last week admitted he would have been a bit insulted if the Giants did not pick up the option.

“But I’ve been hearing this NFL thing is all a business, so I definitely can’t take it personal,’’ said Amukamara, 26, who was a first-round pick in the 2011 draft.

The Giants now have more time to work out a long-term extension with Amukamara, a move that would decrease an unwieldy 2015 salary cap number.

“Who wouldn’t want the fifth-year option?’’ Amukamara said. “It shows that the team wants you, and who doesn’t want to feel wanted?”